U.S. Pat. No. 4,975,354 issued Dec. 4, 1990, entitled "Photographic Element Comprising An Ethyleneoxy-Substituted Amino Compound And Process Adapted To Provide High Contrast Development", by Harold I. Machonkin and Donald L. Kerr, describes silver halide photographic elements having incorporated therein a hydrazine compound which functions as a nucleator and an amino compound which functions as an incorporated booster. Such elements provide a highly desirable combination of high photographic speed, very high contrast and excellent dot quality, which renders them very useful in the field of graphic arts. Moreover, since they incorporate the booster in the photographic element, rather than using a developing solution containing a booster, they have the further advantage that they are processable in conventional, low cost, rapid-access developers.
Other patents describing silver halide photographic elements comprising a hydrazine compound which functions as a nucleator and an amino compound which functions as an incorporated booster include U.S. Pat. No. 4,914,003 and U.S. Pat. No. 5,030,547.
High-contrast photographic elements of the type described hereinabove are typically processed in aqueous alkaline developing solutions containing a dihydroxybenzene developing agent, such as hydroquinone, and an auxiliary super-additive developing agent. Examples of useful auxiliary super-additive developing agents are aminophenols and 3-pyrazolidones. Thus, for example, in the working examples of U.S. Pat. No. 4,975,354, the developing solution comprises hydroquinone and 1-phenyl-4-hydroxymethyl-4-methyl-3-pyrazolidone and in the working examples of U.S. Pat. No. 4,914,003 and U.S. Pat. No. 5,030,547 the developing solution comprises hydroquinone and N-methyl-p-aminophenol.
While development processes based on the use of hydroquinone generally provide very good results with high contrast elements containing both a hydrazine compound and an amino compound, they are disadvantageous with regard to ecological and environmental considerations. In particular, hydroquinone and its derivatives, and the oxidized forms thereof, have become of increasing concern in recent years from the point of view of potential toxicity and environmental pollution. Thus, there is an urgent need in the art for a development process, useful with such elements, which utilizes a developing solution that is highly stable, which exhibits high developing capacity, which does not promote excessive generation of pepper fog, which is resistant to silver sludging and which otherwise meets all the needs of this art, yet which is more ecologically favorable than the developing solutions utilized heretofore because it does not require the use of hydroquinone.
A variety of black-and-white development processes utilizing hydroquinone are currently in commercial use. These range in complexity from simple rapid-access processing--where development of the exposed grains is carried to completion via direct reduction by the developing agent--to more complicated ultra-high-contrast graphic arts processes. For example, contrast enhancement for graphic arts applications can be achieved by development of originally unexposed silver halide grains through a series of imagewise, nucleator-driven fogging reactions. In these more complex, ultra-high-contrast processes, hydroquinone plays key roles beyond the direct reduction of silver halide to metallic silver. For example, at the pH level of 10.0 to 10.5 typically employed in ultra-high-contrast development processes, deprotonation of hydroquinone is such that significant buffering of the developing solution comes from the hydroquinone itself It is also well known that aerial oxidation of hydroquinone, and subsequent sulfonation of oxidized hydroquinone, results in a pH increase. On the other hand, development of silver halide by hydroquinone has the effect of lowering pH. Thus, a hydroquinone developer may show either a pH rise or a pH decrease with practical seasoning; with the amount of the pH shift depending on the balance between the amount of hydroquinone that is aerially oxidized versus the amount of hydroquinone oxidized by the development of silver halide. Developing solutions containing hydroquinone thus offer the potential, at least, of maintaining a stable pH position with seasoning.
A significant level of sulfite is required in developing solutions containing hydroquinone, generally two to three times the molar level of hydroquinone is recommended. Sulfite helps to reduce the rate of aerial oxidation and removes colored oxidation products of hydroquinone by means of sulfonation reactions. Sulfite lowers the rate of aerial oxidation of hydroquinone by the scavenging of reactive intermediates and by an equally important effect of decreasing oxygen solubility and thereby lowering the rate of reaction between oxygen and hydroquinone.
From the above discussion, it is apparent that the role of hydroquinone in the development of nucleated high contrast photographic elements is a complex one and equally apparent that it is very difficult indeed to meet the needs of this art with a developing solution that is free of hydroquinone.
It is toward the objective of providing an improved developing solution, and an improved process for the high-contrast development of nucleated photographic elements, that the present invention is directed.